rcmd(3)
NAME
rcmd, rresvport, iruserok, ruserok, rcmd_af, rresvport_af, iruserok_af, ruserok_af - routines for returning a stream to a remote command
SYNOPSIS
#include <netdb.h> /* Or <unistd.h> on some systems */
int rcmd(char **ahost, unsigned short inport, const char *locuser,
const char *remuser, const char *cmd, int *fd2p);
int rresvport(int *port);
int iruserok(uint32_t raddr, int superuser,
const char *ruser, const char *luser);
int ruserok(const char *rhost, int superuser,
const char *ruser, const char *luser);
int rcmd_af(char **ahost, unsigned short inport, const char *locuser,
const char *remuser, const char *cmd, int *fd2p,
sa_family_t af);
int rresvport_af(int *port, sa_family_t af);
int iruserok_af(const void *raddr, int superuser,
const char *ruser, const char *luser, sa_family_t af);
int ruserok_af(const char *rhost, int superuser,
const char *ruser, const char *luser, sa_family_t af);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
rcmd(), rcmd_af(), rresvport(), rresvport_af(), iruserok(),
iruserok_af(), ruserok(), ruserok_af():
Since glibc 2.19:
_DEFAULT_SOURCE
Glibc 2.19 and earlier:
_BSD_SOURCE
DESCRIPTION
The rcmd() function is used by the superuser to execute a command on a remote machine using an authentication scheme based on privileged port numbers. The rresvport() function returns a file descriptor to a socket with an address in the privileged port space. The iruserok() and ruserok() functions are used by servers to authenticate clients requesting service with rcmd(). All four functions are used by the rshd(8) server (among others). rcmd() The rcmd() function looks up the host *ahost using gethostbyname(3), returning -1 if the host does not exist. Otherwise, *ahost is set to the standard name of the host and a connection is established to a server residing at the well-known Internet port inport. If the connection succeeds, a socket in the Internet domain of type SOCK_STREAM is returned to the caller, and given to the remote command as stdin and stdout. If fd2p is nonzero, then an auxiliary channel to a control process will be set up, and a file descriptor for it will be placed in *fd2p. The control process will return diagnostic output from the command (unit 2) on this channel, and will also accept bytes on this channel as being UNIX signal numbers, to be forwarded to the process group of the command. If fd2p is 0, then the stderr (unit 2 of the remote command) will be made the same as the stdout and no provision is made for sending arbitrary signals to the remote process, although you may be able to get its attention by using out-of-band data. The protocol is described in detail in rshd(8). rresvport() The rresvport() function is used to obtain a socket with a privileged port bound to it. This socket is suitable for use by rcmd() and several other functions. Privileged ports are those in the range 0 to 1023. Only a privileged process (on Linux: a process that has the CAP_NET_BIND_SERVICE capability in the user namespace governing its network namespace). is allowed to bind to a privileged port. In the glibc implementation, this function restricts its search to the ports from 512 to 1023. The port argument is value-result: the value it supplies to the call is used as the starting point for a circular search of the port range; on (successful) return, it contains the port number that was bound to. iruserok() and ruserok() The iruserok() and ruserok() functions take a remote host's IP address or name, respectively, two usernames and a flag indicating whether the local user's name is that of the superuser. Then, if the user is not the superuser, it checks the /etc/hosts.equiv file. If that lookup is not done, or is unsuccessful, the .rhosts in the local user's home directory is checked to see if the request for service is allowed. If this file does not exist, is not a regular file, is owned by anyone other than the user or the superuser, is writable by anyone other than the owner, or is hardlinked anywhere, the check automatically fails. Zero is returned if the machine name is listed in the hosts.equiv file, or the host and remote username are found in the .rhosts file; otherwise iruserok() and ruserok() return -1. If the local domain (as obtained from gethostname(2)) is the same as the remote domain, only the machine name need be specified. If the IP address of the remote host is known, iruserok() should be used in preference to ruserok(), as it does not require trusting the DNS server for the remote host's domain. *_af() variants All of the functions described above work with IPv4 (AF_INET) sockets. The "_af" variants take an extra argument that allows the socket address family to be specified. For these functions, the af argument can be specified as AF_INET or AF_INET6. In addition, rcmd_af() supports the use of AF_UNSPEC.
RETURN VALUE
The rcmd() function returns a valid socket descriptor on success. It returns -1 on error and prints a diagnostic message on the standard error. The rresvport() function returns a valid, bound socket descriptor on success. It returns -1 on error with the global value errno set according to the reason for failure. The error code EAGAIN is overloaded to mean "All network ports in use." For information on the return from ruserok() and iruserok(), see above.
VERSIONS
The functions iruserok_af(), rcmd_af(), rresvport_af(), and ruserok_af() functions are provide in glibc since version 2.2.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7). ┌────────────────────────────┬───────────────┬────────────────┐ │Interface │ Attribute │ Value │ ├────────────────────────────┼───────────────┼────────────────┤ │rcmd(), rcmd_af() │ Thread safety │ MT-Unsafe │ ├────────────────────────────┼───────────────┼────────────────┤ │rresvport(), rresvport_af() │ Thread safety │ MT-Safe │ ├────────────────────────────┼───────────────┼────────────────┤ │iruserok(), ruserok(), │ Thread safety │ MT-Safe locale │ │iruserok_af(), ruserok_af() │ │ │ └────────────────────────────┴───────────────┴────────────────┘
CONFORMING TO
Not in POSIX.1. Present on the BSDs, Solaris, and many other systems. These functions appeared in 4.2BSD. The "_af" variants are more recent additions, and are not present on as wide a range of systems.
BUGS
iruserok() and iruserok_af() are declared in glibc headers only since version 2.12.
SEE ALSO
rlogin(1), rsh(1), intro(2), rexec(3), rexecd(8), rlogind(8), rshd(8)
COLOPHON
This page is part of release 4.09 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
Opportunity
Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.
Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.
Free Software
Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.
Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.
Free Books
The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.
Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.
Education
Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.
Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.
